1. Field of Invention
The present invention relates to a two-step thermal process for recycling scrap tires and waste or other oils with emphasis on the production of valuable products including overhead light oil, and gas and a carbonaceous material useful as a modifier for bituminous binders and Portland concrete.
2. Background
Upwards of 280 million tires are accumulated annually in the United States and about 65 percent are added to stockpiles, landfills or disposed of by other means. The Environmental Protection Agency estimates there are more than two billion discarded tires in this country. Accidental fires at storage sites have been a continuing environmental problem.
Waste motor and industrial oils also contribute to a hazardous waste disposal problem. An estimated 400 million gallons of waste motor oils are illegally dumped in landfills each year. Reprocessing waste oils to produce "new" recycled oils for the motoring public or industrial uses is not economically feasible because collection expenses and refining costs including waste disposal of residual oil sludge are too high and there is a lack of consumer acceptance for reprocessed oils.
A current scrap tire use is the making of crumb rubber modifier for asphalt cements and this consumes upwards of 1.8 million tires per year; however, in comparison to the supply, this is a minor use. Yet the concept of asphalt modification is a useful field to utilize the products from scrap or waste tire reprocessing.
Since more than 90 percent of the paved roads in the United States utilize asphalt, the potential for asphalt modifiers is great. Asphaltic concrete pavement failures traditionally have reasons associated with rutting, moisture-induced induced damage and embrittlement. Many asphalt modifiers have been proposed. See the classic Barth's Asphalt, Gordon and Breach, N.Y. 1962, for a discussion of a wide range of tests concerning modifiers. In particular carbon black modifiers have shown considerable success in reducing rutting and low temperature cracking difficulties. For more than a half a century the annual series Asphalt Paving Technology, Viking Press, Eden Prairie, Minn., summarizes much information on using various asphalt modifiers.
Asphalt when used for its intended purposes often suffers from premature failure due to factors such as aging, embrittlement, or loss of adhesion or cohesion properties. Much development has occurred to improve its performance and rheological properties. However in such instances, asphalt road life is still much less than desired. In recent years numerous advantages have been found for incorporating some form of rubber modifier into asphalt. The rubber gives the asphalt improved elastic behavior, increases its ductility, reduces is susceptibility to temperature changes, and in addition, can improve the surface life of roads.
In order to improve asphalt durability, many rubber-like polymers; such as neoprene, GRS rubbers, latex, nitrile rubber, butyl rubber, natural rubber, and others; have been blended, usually at a composition of a few percent, with asphalt in a conventionally mixing operation; see Barth referenced above.
Direct combustion processes use an estimated 25 million tires annually. Although tires have a high heating value of 15,000 BTU/lb, their economic value as a fuel diminishes because tires contain about 2.5 wt % sulfur. Facilities that use scrap tires as a supplemental fuel source often blend them with coal to keep sulfur pollutants in the stack gas within tolerable levels. Higher levels of sulfur pollutants would require stack gas clean-up which jeopardizes the economics of using tires as a fuel supplement. Further problems arise in combusting waste tires due to their fiber and wire, usually steel, content. Particularly shredded waste tires must overcome this fiber and wire tangling problem with processing machinery.
Pyrolysis, which normally implies thermal degradation at 900.degree.-1400.degree. F. in an inert atmosphere, has been tested both in the laboratory and in pilot-scale equipment to produce either hydrocarbon gases or oils plus a coke-like residue of carbon black. Direct pyrolysis of tires has a disadvantage in that gaseous products generally contain moderate levels of hydrogen sulfide and liquid products contain substantial amounts of chlorinated materials. The presence of chlorinated materials in the oil reduces its value as a refinery feed stock for hydrogenation and other processes. Even low levels of chlorinated materials in feed oils result in process corrosion problems in vessels and piping.
Although many forms of distress in asphaltic and concrete pavements have been identified and solutions sought, problems continue to exist either because the solutions are inadequate or because new variables causing distress manage to stay ahead of the research. Increased traffic and vehicular loads coupled with increased tire pressures have greatly contributed to pavement distress, reduced safety, and increased maintenance costs. These problems associated with permanent distortions, commonly referred to as rutting, in bituminous pavements are further compounded by the effects of moisture-induced damage or moisture sensitivity. Moisture damage, embrittlement, crack formation with adhesion loss between the bituminous binder and the mineral aggregates and rut formation are four major causes of pavement failures. A solution to any one of these problems would have a profound effect in increasing the service life of our roadways and simultaneously provide added benefits to the motoring public.
Surface areas covered with Portland concrete also experience similar forms of distress and high maintenance costs. Crack formation during drying and/or curing modes coupled with load induced failures contribute significantly to maintenance costs. Air encapsulation in Portland concrete increases porosity and permeability of the concrete which allows penetration of salts and water into the concrete structure thereby facilitating corrosion of the steel reinforcing structure. Portland concrete adheres poorly to oily metallic surfaces such as those found in sealing of oil wells. In frigid climates the natural deicing characteristics are inadequate simply because concrete is a poor absorber of solar energy.
Potential United States patents covering the above mentioned concepts include:
______________________________________ U.S. Pat. No. Inventor Year ______________________________________ 5,095,040 Ledford 1992 5,084,141 Holland 1992 5,070,109 Ulick et al 1991 5,060,584 Sowards et al 1991 5,041,209 Cha-1 et al 1991 4,983,782 Mertz et al 1991 4,983,278 Cha-2 et al 1991 4,960,440 Betz 1990 4,895,083 McDilda 1990 4,894,140 Schon 1990 4,867,755 Majid et al 1989 4,806,232 Schmidt 1989 4,787,321 Schnellbacher et al 1988 4,746,406 Timmann 1988 4,686,008 Gibson 1987 4,686,007 Lyakhevich et al 1987 4,647,443 Apffel 1987 4,560,414 Kikegawa et al 1985 4,515,659 Wingfield et al 1985 4,383,151 Audibert et al 1983 4,332,932 Harada et al 1982 4,25O,158 Solbakken et al 1981 4,211,576 Yan 1980 4,166,049 Huff 1979 4,153,514 Garrett et al 1979 4,123,332 Rotter 1978 4,030,984 Chambers 1977 3,978,199 Maruhnic et al 1976 3,915,581 Copp 1975 3,907,582 Walter 1975 3,875,077 Sanga 1975 3,873,474 Ficker 1975 866,758 Wheeler 1907 ______________________________________
Referring to the above list, Ledford disclosed rotary kiln processing of shredded tires with 1000.degree. F. inlet and 800.degree. F. outlet using indirect gas heating.
Holland disclosed waste tire processing by preheating and then microwaving. Microwave energy used to break carbon-carbon bond.
Ulick et al disclosed processing rubber tires using aromatic hydrocarbon oil at up to 600.degree. F. Products obtained were a grease-like and putty-like material which were added to asphalt to improve low-temperature flow properties.
Sowards et al disclosed combusting shredded tires with limestone to control SO.sub.2 emissions.
Cha-1 et al disclosed processing heavy oil using inclined screw pyrolysis reactors and obtaining light, middle and heavy distillates and asphalt binder. Limestone added to remove sulfur containing components from gases.
Mertz et al disclosed waste treatment of old tires with basic addition, such as lime, to trap acidic gases including SO.sub.2, NO.sub.2, and HCl.
Cha-2 et al disclosed processing oil shale, tar sand, waste motor oil, or waste tires for pyrolysis products with recycling of selected distillates. Pyrolysis temperature up to 800.degree. F. Scrap tire process used inclined screw pyrolysis reactor and waste motor oil with magnetic separation of scrap metals. Screw reactors were symmetrically housed. Carbon black obtained used for asphalt modifier.
Betz disclosed producing pyrolysis gas from used tires with a fluidized bed. Sulfur cleanup was employed by adding a basic binder, such as calcium carbonate, hydrated lime, calcium oxide, magnesium carbonate, magnesium oxide, magnesium hydroxide, dolomite, sodium carbonate or sodium hydroxide.
McDilda disclosed combustion of tires and recovery of products from the gases.
Schon disclosed processing waste oil by itself.
Majid et al disclosed reduction of sulfur emission during combustion by the addition of limestone, lime or hydrated lime.
Schmidt disclosed desulfurization of H.sub.2 S from used oil pyrolysis with basic additive and metal to catalyze H.sub.2 S removal.
Schnellbacher et al disclosed apparatus for chopped old tire combustion using ash grate with rotating fingers and operating temperature of 150.degree.-700.degree. F.
Timmann disclosed a pyrolyzing system for tires to produce increased C-4 components by condensing light oil fraction at near 32.degree. F.
Gibson disclosed apparatus for pyrolysis of shredded tires using partial flight screw with oil jet spray and temperature range employed was 1000.degree.-1400.degree. F.
Lyakhevich et al disclosed shredded tire processing at 150.degree.-500.degree. C. with solvent injection through nozzles.
Apffel disclosed carbon black from tires, no oil added, obtained using preheated steam and pyrolysis by hot gas at 2000.degree. F.
Kikegawa et al disclosed asphalt modifier of Trinidad Epure with pulverulent solid, such as lime or gilsonite, for high temperature performance.
Wingfield et al disclosed catalyze pyrolyric conversion of waste rubber with basis salt, such as sodium carbonate, producing increased amount of C.sub.1 -C.sub.4 olefinic materials including isobutylene.
Audibert et al disclosed heating whole tires in oven while spraying with hot heavy oil that was recycled. Temperature of operation was 350.degree.-500.degree. C. with 10:1 ratio of oil to whole tires.
Harada et al disclosed screw extruder for melted waste rubber at 400.degree.-500.degree. C. using no added oil.
Solbakken et al disclosed fragmented used tires pyrolyzed under vacuum with oxygen-limited. Main product was carbon black with tar refluxed. Reactor temperature range was 750.degree.-1800.degree. F. with pressure 1-20 psia.
Yan disclosed dissolving scrap tire rubber in thermally stable highly aromatic solvent with heating at 350.degree.-850.degree. F. until homogeneous and using as asphalt modifier.
Huff disclosed rubberized asphalt made from reclaimed rubber from scrap tires containing critically 30-40% second acidaffins.
Garrett et al disclosed process using shredded waste tires heated to 300.degree.-2000.degree. F. with desulfurization by adding solid sulfur acceptor, such as lime or iron oxide.
Rotter disclosed direct pyrolysis of shredded tires at 400.degree.-900.degree. C. by indirect oxygen-free combustion gas using equipment with staggered paddle-like impeller.
Chambers disclosed using hot gas at 600.degree. F. for melting of whole scrap tires with a wet scrubber for gas cleanup. Carbon black produced at 1100.degree. F. under vacuum conditions.
Maruhnic et al disclosed carbon black production from tires using aromatic solvent at 500.degree.-700.degree. F., 25-100 psig, and filter collection.
Copp disclosed carbon black reinforced polymer used as modifier for asphalt paving.
Walter disclosed asphalt modification with additives of lime and residue from refuse incinerator.
Sanga disclosed waste tire production for activated charcoal using limestone to produce CO atmosphere for product conversion of carbon to activated charcoal. Temperature of decomposition was 400.degree.-800.degree. C.
Ficker disclosed comminuted scrap rubber through heated feed screws at 140.degree.-300.degree. C. using differential gearing with interleaved helical threads; one with twice the pitch.
Wheeler disclosed reclaiming scrap rubber with superheated steam at 600.degree. F.
Foreign patents of interest include Lengd, SU 0644802, 1979, who disclosed making asphalt with the addition of limestone powder and shale processing residue. Yarosl, SU 979125, 1982, disclosed using zinc oxide with rubber to improve solubility in organic solvents.
Asphalt is a viscoelastic material which means it exhibits both viscous and elastic behavior and displays a time dependent relation between an applied stress and the resultant strain. Thus when testing asphalt it is common to refer to the rheological properties as measured by dynamic testing procedures. Rheological testing machines subject a test cylinder of asphalt to a periodic or dynamic loading pattern involving a sinusoidal input on one end and measure the resulting response on the opposite end which now is out of phase with the input. Thus the shear modulus, G*, has a real and an imaginary component, G' and G". The rheological results are usually expressed in terms of the following: EQU Loss tangent=tan (delta)=G"/G' EQU Complex shear modulus=.vertline.*.vertline.=[(G').sup.2 +(G").sup.2 ].sup.1/2 EQU Dynamic viscosity=eta*=.vertline.G*.vertline./omega
where delta is the phase angle and omega the applied strain frequency. See Ferry, Viscoelastic Properties of Polymers, John Wiley, N.Y. 1961; or Goodrich, "Asphalt and Polymer Modified Asphalt Properties Related to the Performance of Asphalt Concrete Mixes," Asphalt Paving Technology 1988, 57, pp 116-126, Viking Press, Eden Prairie, Minn., 1988. Properties of asphalt binders with and without modifiers generally are expressed in these rheological terms.